Rhododendrons

How to choose a rhododendron

The hardy hybrids are the reliable garden types. The Pink Pearl Rhododendron has large pink trusses that fade to white, the Sappho Rhododendron is white with a dark blotch, the President Roosevelt Rhododendron has variegated foliage and red flowers, and the Purple Splendour Rhododendron carries deep purple flowers.

The Native Rhododendron (Rhododendron lochiae) is one of only two rhododendrons native to Australia, a small shrub from the rainforest of far north Queensland with red bell shaped flowers. It suits a warm, humid, sheltered position, and is quite different from the hardy hybrids.

Where rhododendrons grow

The hardy hybrids do best in cool to mild temperate climates, such as the Dandenongs, the Blue Mountains, the Adelaide Hills, southern Tasmania and Canberra, in part shade with protection from afternoon sun. They do poorly in hot, humid subtropical and tropical gardens, where root disease and heat stress are common. If you live in a warm northern climate, the native species or a pot position under shade is the better route.

Rhododendrons pair well with azaleas, camellias and hydrangeas, which all enjoy similar soil and shade.

Rhododendrons are slow growing in most gardens and many are long lived, so they reward patience. Mature hybrids typically reach one and a half to three metres, and they look best in drifts or as a backdrop to a shaded path, beneath tall trees that give dappled light.

Planting and spacing

Rhododendrons have shallow, fibrous roots, so plant them high, with the top of the root ball slightly above the soil surface, in soil rich in organic matter. Add acidic compost, and avoid lime. Space plants about 1.5 to 2 metres apart, and mulch generously with leaf litter or bark, keeping it off the stem.

Care basics

Water regularly, especially in the first two summers, because the roots dry out quickly. Feed after flowering with a fertiliser made for acid loving plants. Deadhead spent trusses to save energy for next year, and prune lightly straight after flowering. Yellowing leaves between the veins often point to alkaline soil or poor drainage.

All parts of rhododendrons are toxic if eaten, to people and animals, so keep pets and children away from the leaves and flowers.

Planting under the canopy of established trees gives the dappled shade and leaf litter that rhododendrons enjoy, but avoid sites where tree roots compete heavily for water.

Common questions

When do rhododendrons flower?

Mostly from late winter to late spring, depending on the variety and your climate.

Do rhododendrons need acidic soil?

Yes. A soil pH of about 5 to 6 suits them. In alkaline soil, grow them in a pot of acidic mix.

Can rhododendrons grow in full sun?

In cool climates, a morning sun position is fine. In warm areas they need shade from the afternoon sun.

Can I grow a rhododendron in Queensland?

The native species is the better option in the warm north, since the hardy hybrids struggle in heat and humidity.